But I would like to extend this snippet template to handle infinite fields. I can see no system that facilitates this in ST, as a system like this needs to repeat blocks of text.

I imagine the system would need to adapt the $ token to indicate a repeating block.The {} brackets would define the repeating block(s) A repeat trigger character would also need to be defined to indicate when another repetition should be started.In the case of the value class example the repeat character would be a comma ','

The way this is usually handled is to make a snippet that inserts a new instance of it's own snippet trigger as last tab target. In that way you just press tab again to continue expanding it. Something like this:

There might be something in there which will set you along the right path to duplicate blocks of code. I am a front-end markup and UX guy so the Python and JavaScript code is too heavy going for me to steer you any further. If you do use this, and find a solution please post back. It would certainly come in useful for some of the advanced markup snippets I have written to be able to replicate code 'X' amount of times on the fly. Best of luck.